I'm almost always shorter than my sparring partners (at ~5'7") and my go-to approach is to slip forward and to the outside while throwing a bodyshot. If they're othrodox, when they throw the left, I slip ahead and to the right with a stiff left to the body. If they're lefty, when they throw the right jab, I slip ahead and to the left with either a stiff right to the body. If you get outside and close like that, it's relatively easy to pivot back toward the center and hit them with an overhand from a dead angle. I practiced this without the counterpunch initially; I would have my partners throw the jab and I would try to slip and close as fast as possible, to smother any chance they had to continue throwing. They would have to reset their position to get a bead on me again, and that's a great time to be hitting them.

Thanks for the advice everyone! I tried every single suggestion and guess what? Most of them worked! The footwork suggested by WhiteShark in particular I found particularly effective but every input is appreciated....thank you :)